The invention relates to a method for steering an aircraft by controlling separated vortical flows at the leading edges of an airfoil by means of movable flaps or streams at the leading edge of the airfoil.
The air flow over slender, aerodynamic surfaces, for example, surfaces with delta, arrow or gull wing, or ogive, or gothic wing configuration, is dominated beyond a certain angle of attack by the occurrence of stable, concentric vortical sheets. The vortical sheets are being rolled up over the airfoil with a shape similar to a funnel. The vortical flow starts at the leading edge of the lifting surface, wing, or airfoil. The occurrence of such vortical flow depends on the sweep back and the nose structure of the lifting surface, that is, the curvature, and so forth as well as the smoothness of the contour or strake of the nose structure. The sweep back, the nose structure, and the strake influence the angle of attack or rather they determine the size of the angle of attack beyond which the flow characteristics have a nonlinear dependence on the geometric angle of attack, whereby an additional lift occurs, which is dependent on the angle of attack of the lifting surface or the wing.
German Pat. No. 699,157 illustrates examples of such wing forms, which produce a lift that may be varied by adjusting the position of wing components in response to the air pressures occurring at the upper side and at the lower side of the wing nose. The pressure difference existing in this instance, between the upper side and the lower side is caused by the positive pressure at the lower side and the negative pressure at the upper side of the wing, whereby the angle of attack of the entire wing is increased.
The most varying methods for utilizing or gaining an additional lift have been proposed heretofore. For example, the German Patent Publication (DOS) No. 1,506,598 suggests constructing the leading edges of the wings as a special gap-camber flap. The German Patent Publication (DOS) No. 1,917,532 develops this idea further by constructing two extendible flap members so as to form a gap. All of the above proposed solutions for obtaining additional lift have the disadvantage, that the total nonlinear additional lift may not be utilized completely because the steering capability and the stability about the roll and yaw axes are very quickly and prematurely lost at the angle of attack required for such full utilization of the supplementary lift.